The present invention relates to systems for dispensing strap from a coil and, in particular to a strap accumulator for such dispensing systems. While the invention may be used with any type of strap, it has particular application to plastic strapping.
Strap for binding packages, boxes, bundles, coils of wire, and the like, is supplied from the finishing mill in coils described as "mill wound" and ribbon wound". A mill-wound coil is one having a thickness greater than the strap width, usually three to six times as thick, and wherein the strap convolutions crisscross so that strap is evenly distributed throughout the coil. A ribbon-wound coil has a thickness equal to the width of the strap, and each convolution exactly overlies the next.
Many coils tend to be quite heavy and have considerable inertia. Accordingly, when strap is unwound from such a coil for use by a strapping machine or the like, the inertia tends to produce considerable shock on the strap feeding mechanism of the associated strapping machine. This is particularly true of mill-wound coils which are typically heavier than ribbon-wound coils of comparable diameter. Thus, in the start-stop mode of operation of a typical strapping machine, considerable energy must be expended to repeatedly restart the rotation of the coil for unreeling thereof, and this energy must repeatedly be dissipated by braking mechanisms or the like to avoid overrun of the coil and resultant tangling of the strap.
In order to alleviate these problems, it is known to use strap accumulating devices between the coil dispensing mechanism and the associated strapping machine. In such accumulating devices the strap is unreeled from the outside of the supply reel and is fed loosely into the accumulator, which accumulates a supply of the strap. The strapping machine withdraws strap from the accumulator at high speed with virtually no resistance. A separate power feed wheel draws strap from the supply reel to replenish the accumulator, usually at a slower rate. One such accumulator which is widely used with plastic strap is in the form of a narrow box having a width only slightly greater than the width of the strap. The strap is pushed into one side of the box and it piles up inside the box, being continually folded back upon itself in random fashion, the strap being withdrawn from the other side of the box.
A disadvantage of this random type of accumulation, particularly in the case of plastic strap, is that the strap forms fairly tight curves at the folds. This results in random curl in the strapping material, particularly if it is left in its folded condition for a protracted time, such as overnight. This random curl can result in malfunctioning of the strapping machine upon start up. Furthermore, in such box-type accumulators, there is a large amount of wasted space and the ratio of accumulated strap length to accumulator volume is relatively low.